Injector mechanism



Sept. 2, 1952 M. D. MARTIN INJECTOR MECHANISM Filed Oct. 11, 1950 INVENTOR. MA/PV/N D. MART/N i atenteti Sept. 2

UNITED STATES PATENT OFFICE 2,509,500 mmcron MECHANISM Marvin D. Martin,Berkeley, Calif, assignor to the, United States of America asrepresented. by the United States Atomic Energy Commission ApplicationOctober 11, 1950, Serial No. 189,642- 8 Qiaims, (Cl. 2250-27) 1 The sennv n on r ates enerall t particle accelerators andginmore particular tom r m nts n ie to s or sv h onsaod the like.

The injection of char ed Particles; into particle accelerators andsimiliar apparatus that constrain ar ed particlest e v rs ubst ntiallycircular orbits often interferes with the subsequent acceleration of theparticles in that the injector mechanism is, of necessity, located inclose proximity to the-particle orbit. This is particularly true insynchrotrons which cona n e ted ar icles o r n. tsuo constant radiusthat therefore approach the-inm han sm endilifitmw w th. rei r n s to pai e er rs o th hrotron. t e

that the invention isdisclosed and described.

Considering first the magnitude of interference normally resulting fromthe injector mechanism of a synchrotron, it is noted that maximum.injector efliciency is obtained with the injector mechanism locatedapproximatleyon the circular orbit of the accelerated particles.

In 'a typical synchrotron operatiQn electrons areaccelerated about aconstant radius orbit wherein, for example, they. traverse the orbitabout 25 times each microsecond and an aceelerating1 cycle lasting 8,000.rnicrosecends requires 200,000 complete trayersals of the orbit withinthis time. It, will be appreciated that only the relatively fewelectrons whichfollow displaced orbits} or orbits. deviating from"normal will complete thev above accelerating cycle. Thus only thesefewelectrons constitute, the final accelerated beam and comprise usefuloutput of the. apparatus Numerous synchrotron modifications have inthepast been developed for the purpose oi overcoming the above-notedproblems and these modifications have proven more or less advanr tageouswith the maximum increase in the output beam being of the order of 50%.While such an increased output is undoubtedly desirable,

the modifications generally relate to magnet modifications or theaddition of expansion coils V which not. only add to the complexity. andcost of the acceleration apparatus but also contain inherent limitationswhich limit further improvement in. the; accelerator efficiency.

The present invention accomplishes. injection without interference withsubsequent particle acceleration, in a mannerexplained in detail belowand in conformity with. thefollowing objects.

t s. an je o th p es n nven io o pro e a e nd im o ed Wehrmacht-- et. P.net le eee ler wra- It amt e bie of e er se t nvent on to provide animproved inj ctor mechanism {or particle accelerators which does notinterfere with particle acceleration.

t is a e bieet i e; s nt m n ion to provide synchrotron injectormechanism ca: p e of r v n a le im i ement thereon.

It is. st a ot object ofthe masco in n tion to provide-an improvedinjector mechanism r Pa ticle ac e r to a d n lu i n. e e

ati field gu din ac elera ed. articl s. past a d n ec mec an m- It e anoher b e f hemesen i ven: e; *9- P IQ im r ved m th d t n ect:

a icl s t a pa cce er or w ere n e ac eler t on 0 arfiqle no m ded bythe injection.

It is a further object oi the present invention l o provide an mproved sn h r in ctor seha sm v a le r s at ie d u ding accelerated particlesabout the injector.

It is a still further object of the present ine vention to provide animproved synchrotron i;n.

jectormechanism having an integral accelerat ing field further employedto guide accelerated pa i l s, as hei i e rc mp sh d. s. f ll s t f r hn hefol w e;

e c o f nstr qtiqnr a e at onw i il t n er d h n o sider d i lQQDr Jun iwith a om any ng; drawin s...

wherein:

F ure 1 is a l n i w t e in to mesh? m srn in section;

F is a e eleva o of he. i ect r l p.

partially broken away and including a simplified representation of anassociated electrical sys-l tern; and i Fig. 3 is a plan view 'of asynchrotron chamber showing the injector mechanism inposition.

Referring first to an injector mechanism as shown in Figs. 1 and 2, itwill be noted that there;

c or nd. orm dte el etron misthereto.

m ns o h re i:

he m erin h c the a o e s are is provided a filament ll heated byelectrical shield l3 and surrounding same is an accelerating electrodeI6 which may be formed in the general shape of a square truncated conewith a closed small end or may alternatively comprise a generallyU-shaped plate disposed about shield [3 as shown in Fig. 1. Electrode 16has an elongated aperture I'I therein in general alignment with theaperture l4 in shield I3 and preferably of a greater width toaccommodate the passage of a slightly divergent beam of electrons. Asecond aperture [8 in electrode [6, of the same size as aperture I1, isprovided on'the opposite side of filament H and shield [3 from apertureH. In the illustrated embodiment of the invention, strengthening of thetip of electrode [6 may be accomplished by the .use' of braces I9.

filament current supply 3|, electrons are thermally emitted from thesurface of filament l l in copious quantities. Filament H and associatedconductors 12 are electrostatically shielded by shield member l3 exceptfor one face of filament II which lies adjacent aperture l4 in shield13. The relatively high positive potential upon accelerating electrodel6 establishes an electrostatic field which, acting through aperture I4in shield 13', attracts electrons formed at filament ll. Under theinfluence of this field, electrons at filament II are acceleratedthrough aperture [4 in shield I3'toward electrode I6. and thence throughaperture l1 therein. These electrons emerge from the injector mechanismwith a ceri tain minimum velocity and a small divergence in secured toelectrode l6 across the ends of aper- I tures I1 and [8.

The above-described injector elements may be secured in position by anysuitable means such as,"for example, the mounting arrangementillustrated in Fig. 1. As shown, electrode [6 is provided with a flangeextending outwardly from the-open; end thereof, and this flange issecured as bysoldering to a plate 2|, which is in turn mounted upon pins22, as shown. Extending into the synchrotron chamber 23, as shown inFig. 3,- is an insulating stem 24 having indentations upon the inner endthereof into which pins 22 -mate to provide support for electrode 16.Within insulating stem 24 there is provided a second elongatedinsulating member 26 through which filament leads I2 pass in rigidrelation thereto and upon which is mounted shield member- 83-, as'byclamping means 21. Synchrotron chamber 23 is made vacuum tight aboutstem 24 and insulating member 26 by any suitable means, not shown, inorder that particle acceleration. may be accomplished in a high vacuum.

The elements of the injector are maintained at particular potentialsrelative to each-other in order that they may accomplish theirfunctions, as briefly stated above and more specifically explained belowinthe description of operation. As shown schematically in Fig. -2, afilament current supply 3| is connected between filament leads 12 toprovide heating current for filament I I. -Shield I3 is electricallyconnected to filament ll-tomaintain each at the same potential, andpotential supply means '32 is electrically connectedbetween electrode [6and shield-l3. In the embodiment of the invention illustrated,electrons-are produced at filament II for acceleration and in thisinstance electrode I6 is maintained at a positive potential with respectto shield l3 and filament II by potential supply means 32 for thepurpose of attracting electrons from filament II. It will beappreciated, however, that the relative potentials of the elements ofthe injector are determined by the type of particles to be accelerated,and also the type of source employed may be varied in order to producethe desired'type of particles.

Considering now the operation of the invention, attention is firstdirected to the fact'that the inje'ctor' mechanism contemplates ejectionof charged particles into a chamber or other envelope wherein theseparticles are more or less separately operated upon. For convenience ofillustration, the following explanation i with ref erence to synchrotronoperation wherein electrons expelled from the injector mechanism areconstrained to travel constant radius orbits with increasing velocities.With filament H energized byheating current through conductors [2 fromdirection. Because of this small but unavoidable divergence indirection, these emerging electrons actually follow slightly diiferentorbits which each have the same radii but which have the centers thereofslightl'ydisplaced. For the sake of simplicity, it is desirable toconsider the electrons emerging from the injector mechanism ascomprising a plurality of beams, as illustrated in Fig.

3. As may be seen from Fig. 3, upon completion of one revolution withinthe synchrotron, the dis- I placed electron beams converge upon theinjector mechanism and in the-absence of preventative measures wouldinthe great majority impinge it Will be appreciated that the equipotentiallinesbetween electrode [6 and shield l3 lie generally parallel theretoexcept in the vicinity of apertures'in these elements. Immediatelyadjacent aperture l8 in electrode I6, the equipotential lines are bowedtoward the aperture and in fact equipotential lines directly adjacentelectrode I6. are materially expanded into a bubble which protrudesthrough aperture [8 exterior to electrode [6 much in the mannerillustrated by dashed lines 36 in Fig. 1. This field configurationextends outwardly from the back of the injector mecha-' nism anddirectly affects the orbits of electron beams accelerated in synchrotronchamber 23. As previously noted, the electron beams from the injectormechanism'travel orbits of constant radius which are, however, slightlydisplaced from one another as a result of a small divergenc in thedirection of the electrons leaving the injector mechanism. Thisdivergence is greatly magnified in Figs. 1 and 3, in order to moreclearly illustrate the phenomenon. As will be seen from Fig. 3. thebeams generally converge in the vicinity of the injector mechanism andit i thi portion of the orbits that is depicted by lines 31 in Fig. 1.

.As the electron beams approachthe bubblelike electrostatic fieldprotruding from the back of main slightly deflected toward the center oftheir orbit. This deflection or repelling action is'suflicient to guidea large portion of the electrons 4 around the injector mechanism andthese electrons then continue to revolve about the synchrotron chamberwithout subsequent interference by the in ector mechanism. As -will beseen' from The present invention overcomes this" 1.,isomeview.electronslapnroach the hacker back of the injector mechanism whenaperture i8 is made, the same size as aperture i1 and is exactlyaligned'therewith.

Typical operation of a synchrotron includes electron injection for aperiod of two microseconds, in the course of which some'fiftyrevolutions are made by electrons in the synchrotron. Total accelerationmay last 8,000 microseconds in which time some 200,000 revolutions aremade and with a conventional injector a large percent of the electronsimpinge upon the back of the injector mechanism; however, with thepresent injector the synchrotron output is multiplied some fifteen ormore times over that possible with conventional apparatus.

The above description of the invention is referenced to only one type ofparticle accelerator and is disclosed in terms of but a Singleembodiment; all of which is in no-wise to be taken as limiting but onlyas one illustration of the invention. As it will be apparent to thoseskilled in the art that numerous modifications and variations arepossible within the spirit and scope of the invention, no limitationsare to be taken from the above description but instead attention isdirected to the following claims for a precise definition of the noveltycontained in the invention.

What is claimed is:

1. Particle accelerator injector mechanism comprising an electronemissive filament, a shield about said filament electrically connectedto said filament and having an aperture therein for the passage ofelectrons therethrough, and an accelerating electrode adapted to bemaintained at a positive potential with respect to said shield andfilament and encompassing said shield and filament, said acceleratingelectrode having a first aperture therein aligned with the aperture insaid shield and a second aperture situated on the opposite side of saidshield and filament and aligned with said first aperture.

2. Synchrotron injector mechanism comprising an electron emissivefilament, electrostatic shielding means including first and secondelectrodes surrounding said filament and defining an electron paththerethrough from said filament, said first and second electrodes beingdisposed in part in front and in back respectively of said filament,

and potential supply means connected between said filament and first andsecond electrodes to maintain said first electrode at a positivepotential with respect to said second electrode and filament forattracting electrons from the front of said filament and repellingelectrons from the back of said filament.

3. Synchrotron injector mechanism adapted to be disposed within asynchrotron chamber and comprising an electron emissive filament, anelectrostatic shield about said filament and electrically connectedthereto, said shield having an aperture therein adjacent one face ofsaid filament for the passage of electrons from said filamenttherethrough, and accelerating electrode structure about said shield ata distance therefrom, said accelerating electrode having a firstaperture therein in alignment with said shield aperture and adapted tobe maintained at a positive potential with respect to said shield andfilament whereby electrons emitted fromsaidfilament areulged-xthroughsaid :shield aperture and -,Said:first acceleratingelectrode aperture into said synchroe tron chamber, and saidaccelerating eleetrqflea having .:a second aperture therein ontheopposite sideof said filament and shield andaligned With.-

said first aperture wherebythe positive potential;

of. said accelerating potential. 'isgmodified. in they vicinitylof saidsecond aperture to repel electrons,

approaching said injecto'rmechanism- 4. Synchrotron injector mechanismcomprising; a source of electrons, first apertured-electrode;

means, power-supply means havinga positiv er'tere minal connected tosaid first electrode and a negative terminal connected to said source ofelectrons to establish an electrostatic field for attracting electronsfrom one side of said source, and second electrode means connected tothe negative terminal of said power supply to establish a furtherelectrostatic field exterior to the opposite side of said source of apolarity to repel electrons.

5. A synchrotron injector mechanism including an electron sourcedisposed within a toroidal synchrotron chamber, an aperturedelectrostatic shield about said source and electrically connectedthereto, and an accelerating electrode structure disposed about saidshield to be maintained at a positive potential relative thereto wherebyelectrons are attracted from said source, said accelerating electrodehaving a first aperture therein in alignment with the aperture in saidshield whereby electrons are accelerated therethrough into saidsynchrotron chamber, and said accelerating electrode having a secondaperture in the opposite side thereof from said first aperture and insubstantial alignment therewith to thereby form a relatively negativeelectrostatic field configuration about said second aperture exterior tosaid accelerating electrode from said electrostatic shield for repellingelectrons approaching said injector mechanism.

6. In combination with an electron source having an aperturedelectrostatic shield thereabout, the improvement comprising acceleratingelectrode structure disposed exterior to said shield and having firstand second apertures therein,

said apertures being in substantial alignment said electrostatic shieldand the first aperture in said accelerating electrode structure andelectrons are repelled from said accelerating structure in the vicinityof the second aperture therein by virtue of the relatively negativepotential upon said electrostatic shield.

7. Injector mechanism for apparatus accelerating electrons along aconstant radius orbit comprising an electron source, an aperturedelectrostatic shield about said electron source, electron acceleratingmeans adjacent and exterior to said electrostatic shield for removingelectrons from said source and urging said electrons into the orbit ofsaid apparatus, and electrostatic field producing means for establishingan electron repelling electrostatic field exterior to said ion sourceand shield on the opposite side thereof from the removal of electronswhereby the orbits of said electrons in said apparatus are deformed topass said injector mechanism.

8. An improved injector mechanism adapted 1" for disposition within anevacuated chamber and comprising an electron source, first and secondelectrodes disposed about said electron source,

saidflrst electrode being exposed to said electron source and to saidchamber to define an electron path therebetween and said secondelectrode bes electrons are repelled irom 'the oppos'ite-si de of saidmechanism from-said electronpathf 5 p REFERENCES CITED The followingreferences are of recordin thefile of this patent: l

10 UNITED STATES PATEN'VI'S' Number Name Date H 2,335,014 Kerst Nov.23,1943 V 2,497,891 Kerst Feb. 21,1950

